Brazil's former President Luiz Inacio Lula da Silva has been detained by police over corruption allegations.
Police said on Friday they had evidence that Lula received illicit benefits from a kick-back scheme at state oil firm Petroleo Brasileiro SA (Petrobras) in the form of payments and luxury real estate.
"Ex-president Lula, besides being party leader, was the one ultimately responsible for the decision on who would be the directors at Petrobras and was one of the main beneficiaries of these crimes," a police statement said.
After questioning, da Silva said he feared no one. "If they wanted to hear from me, they only had to call and I would have gone, because I owe nothing to anyone and fear nothing."
"This is not justice, this is violence," he said.
Lula's house near Sao Paulo was raided by authorities early on Friday.
"There is evidence that the crimes enriched him and financed electoral campaigns and the treasury of his political group," said the statement.
Officials said some 33 search warrants and 11 detention warrants were being carried out by 200 federal police agents in the states of Rio de Janeiro, Sao Paulo and Bahia.
Clashes were reported outside Lula's home between groups of rival protesters.
Television images showed Lula's supporters clad in red shirts exchanging chants, insults and even blows with his detractors in the street outside his home.
Police officers beat back some protesters with batons.
Lula's foundation said in a statement on Thursday that the former president had never committed any illegal acts before, during or after his presidential term.
His detention would be the biggest event so far in an investigation of alleged corruption at Petrobras, known as Operation Car Wash,which has snared lawmakers and some of Brazil's most powerful business executives.
Lula, from the Workers' Party, served two terms as president and was succeeded in office by his political protege, Dilma Rousseff.
He ran Brazil from 2003 to 2010, when prosecutors allege much of the graft took place. His detention would tarnish the reputation of the most beloved leader in Brazil's modern history and threatens the government of his successor Rousseff.
Rousseff has also repeatedly denied any wrongdoing.